First, admittedly I'm not sure the cause to your error as I do not have access to your generated SOAP client classes, your SSL Configuration, etc.
That said, I was able to implement the UPS API for the Tracking API and was able to execute without issue. To get it to work you will need to do the following.
1. Create a SSL client configuration (test it against the UPS server) to be used for SSL encryption. it does not appear that UPS provides a non encrypted connection for testing.